The present invention in general concerns improved surge control (i.e., accumulator) apparatus and method, and more particularly concerns improved method and apparatus for providing accumulator operations which positively prevent the occurrence of product shear points, regardless of variations in the exact sizes of products from their nominal size, or the initial position of the products relative the conveyor prior to a product removal operation.
The entire disclosure (including all description and every figure thereof) of Steeber, U.S. Pat. No. 4,989,718, issued Feb. 5, 1991, is fully incorporated herein by reference as if the same subject matter (both by way of background and as to essential subject matter) were presented and recited herein.
A long-term problem in production line operations is to ensure smooth and continuous operation of the production line and components thereof. However, it is well known and widely experienced that various components or workstations along the conveyor or production line may operate at different rates of speed, thereby resulting in a blockage or queue of products developing at one or more points along the production line. In general, the foregoing problem has been addressed by the addition of accumulator devices for temporarily removing and storing products backing up along a production line or conveyor. However, the presence of such devices also in some respects creates an additional component which is subject to breaking down or causing other problems relative the production line. If such occurs, the accumulator device very undesirably becomes a liability to the production line or conveyor rather than the asset and advantage which was intended.
The improved accumulator of the above-referenced '718 patent advantageously addresses many of the general problems of accumulator operations so as to minimize mishandling of products which can result in highly undesirable failed operations of the accumulator. However, one more specific problem faced during accumulator operations is the accommodation of unpredictable variations in the sizes (from their nominal size) of individual products being handled, particularly where such variations cumulatively result in highly significant dimensions relative a line (or slug) of products to be removed from a conveyor. The advantageous methodology and apparatus of the above-referenced '718 patent inherently may accommodate cumulative variations of, for example, up to approximately 3/4 of an inch to perhaps an inch. Such degree of accommodation is entirely adequate in many circumstances. The greater difficulty comes in those situations where the cumulative variations exceed even such amount. When such an excessive situation develops, the result can be the existence of interference (i.e., product shear points) between fixed members of the accumulator and products remaining on the conveyor or being removed therefrom.
One example of an accumulator device which refers to the occurrence of product size variation is Mattei (United Kingdom published Patent Application No. 2170169; published Jul. 30, 1986). It is noted in lines 71 through 77 of page 1 of such publication that slight and unpredictable variations in the size of products can result in variation in the longitudinal dimension of the group of products to be removed such that the group projects beyond the end of an intended storage area resulting in interference with fixed components of the accumulator during storage operations. The Mattei apparatus intends to eliminate such problem by providing an extracting means for literally removing a potential trouble packet from the group of packets to be removed and stored.
The Mattei approach does not necessarily render a positive solution to the situation of excessive growth (or shrinkage). Another difficulty with such approach is the inherent limitation on any device which relies on (or expects) a product with which it interacts being located in a particularly place (within given tolerances). In other words, an extraction device or clamping arrangement of any type which mechanically operates at a predetermined point relative a conveyor can potentially fail to adequately grasp or retain (i.e., engage) an intended packet because of the initial position of such packet relative the mechanism. The result of a near miss can be the creation of an additional shear point or even damage or crushing of one or more packets. Worst case situations can include jamming of the device resulting in failure of the accumulator.
Another facet of the problem generally related to unintended and unpredictable variations in the size of specific packets is the considerable number of different factors which can cause such variations. In order words, such a large number of factors can cause variations that it is virtually impossible to adequately control or eliminate all such factors, wherefore the above-mentioned cumulative variation problem can not as a practical matter be prevented from occurring in an accumulator apparatus.
Using for example products of the type comprising an aseptic paper package filled with liquid (as generally discussed in the above-referenced '718 patent), the following factors are exemplary. In the accumulator operations described in the '718 patent, a slug of products can include a number such as 24, 27, or 30 packages. Variations of, for example, 1/32 of an inch per package can result in significant cumulative differences over the length of the slug. With the accumulator mechanism of the '718 patent, products preferably are systematically held at the outfeed end of the accumulator; hence, the specific location of a product at the outfeed end is established with reasonable certainty. Accordingly, the greater problems of not knowing with certainty the location of a product occurs at the infeed side (i.e., upstream side) of the accumulator mechanism.
One potential variation in the above-mentioned exemplary type of product can occur in the paper being used to make the packages. If a given lot of paper is slightly thicker than a previous lot, the resulting sizes of the cartons will relatively increase, quickly giving rise to the cumulative dimensional problem discussed above. Likewise in the area of package formation, wear in the machine making the package can result in slightly different dimensions of a finished package. For example, if the edge of a fold or creasing member wears over time, then the associated dimension of a package being formed will slightly change. In general, accumulator devices of present constructions and types of operation must be adjusted over time to compensate for wear in the folding mechanisms or the like of such carton forming machines.
Another factor in the area of the paper itself is that shipments of paper from different sources can involve paper of the same thickness, but of slightly softer or slightly more rigid construction. The resulting difference in the finished package is seen as differences in the amount of package compression as they move along the production line, again creating the potential for adverse cumulative dimensional effects.
Another potential factor in the case of liquid filled containers is slight variation in the amount of volume being introduced into the container, which variations can cause the size of the packages to grow or shrink.
Even if the packages themselves are the same, other mechanical factors can affect the cumulative dimensions of a slug of packages. For example, as lubrication on the conveyor belt changes over the course of time, the coefficient of friction for a chain drive or the like for the conveyor may vary, which results in more or less axial (i.e., in the drive direction of the conveyor) compressive forces on the packages, again affecting the position of the packages at the infeed of an accumulator device. Such problem particularly may occur where the accumulator operations take place (as they often do) while the production line or conveyor continues to run. In such instance, the queue or slug of products simply are sliding relative the conveyor, which moves continuously. Accordingly, the potential compression of products is constantly a factor to consider.
Another example of a factor which is not strictly based on variations in the sizes of individual products is that one or more packages may occasionally become tipped while traveling on the conveyor belt. For many packages, the height of the package is greater than (or at least different from) the length of the package when in an upright position. Accordingly, if a package becomes tipped, there can be a considerable change in the cumulative dimension of a group of packages. For example, the occurrence of a single tipped package could be enough to cause a mechanism such as the extraction device of Mattei (UK Patent Application No. 2170169) to entirely miss its intended package (or to grab two adjacent packages). Again, the general problem with such an approach to the overall technical problem is that a deficiency arises if the target or intended package is not precisely in its expected position.
In view of the numerous different factors which can cause or influence the problems associated with cumulative variations in a line or slug of products to be removed from a conveyor with an accumulator apparatus, it is not a practical solution to attempt to address and control all such factors individually so as to prevent the occurrence of the problem in the accumulator apparatus. Nor is it an entirely satisfactory approach in every instance to address the overall problem with mechanisms which depend on the products being at an expected position (within certain limited deviations therefrom). Nor, in general, is it desirable to increase the complexity of existing accumulator devices since added complexity often results in additional breakdown problems, thereby further defeating the overall purpose of the accumulator device.